Meeting Abstract
Teleost fishes have a lower jaw that contains three fused bones: the dentary, angular, and articular. In adults, these bones surround the Meckel’s cartilage (MC). Members of at least ten lineages of teleosts, including derived poeciliids, have an independently derived “extra” joint between the dentary and the angulo-articular, the intramandibular joint (IMJ). The evolutionary morphology of the IMJ is less understood. The IMJ in Poecilia spp. is spanned by the MC, which bends during feeding. Meckel’s cartilage in Poecilia is non-homogenous, where the middle of the cartilage is more cellular with a noticeably less amount of extracellular matrix (ECM) at the location where bending occurs compared to the articulation points with the bones. This non-homogeneity of MC is uncommon among teleosts. Previous studies show that mosquitofish, Gambusia affinis, unlike their poeciliid relatives, do not possess an IMJ; however, the dentary and angulo-articular are not solidly fused in G. affinis, so it is possible that slight intramandibular bending has been undetected in this species. The purpose of this study was to identify the composition of the MC in adult G. affinis to provide clues to the evolution of the IMJ in this lineage. We hypothesized that the MC in G. affinis is also non-homogenous, similar to Poecilia spp., but to a lesser degree given a lack of intramandibular bending during feeding. We found that the MC in G. affinis is homogenous with a similar proportion of cells to ECM throughout the structure, further corroborating that Meckel’s cartilage is not bending in this species. Taken together, these data suggest that in poeciliids, the dissociation of the dentary and anguloarticular may have occurred prior to changes in the cellular morphology of Meckel’s cartilage in the IMJ.
